1013 midpointdistnaceandpythag

Holt McDougal Geometry
1-6
Midpoint and Distance
in the Coordinate Plane
Drill #11 9/17/12
1. Graph A (–2, 3) and B (1, 0).
2. Find CD. 8
3. Find the coordinate of the midpoint of CD. –2
4. Simplify.
4

1-6
Develop and apply the formula for midpoint.
Use the Distance Formula and the
Pythagorean Theorem to find the distance
between two points.
Objectives

1-6
coordinate plane
leg
hypotenuse
Vocabulary

1-6
A coordinate plane is a plane that is
divided into four regions by a horizontal
line (x-axis) and a vertical line (y-axis) .
The location, or coordinates, of a point are
given by an ordered pair (x, y).

1-6
You can find the midpoint of a segment by
using the coordinates of its endpoints.
Calculate the average of the x-coordinates
and the average of the y-coordinates of the
endpoints.

1-6

1-6
To make it easier to picture the problem, plot
the segment’s endpoints on a coordinate
plane.
Helpful Hint

1-6
Example 1: Finding the Coordinates of a Midpoint
Find the coordinates of the midpoint of PQ
with endpoints P(–8, 3) and Q(–2, 7).
= (–5, 5)

1-6
Check It Out! Example 1
Find the coordinates of the midpoint of EF
with endpoints E(–2, 3) and F(5, –3).

1-6
Example 2: Finding the Coordinates of an Endpoint
M is the midpoint of XY. X has coordinates
(2, 7) and M has coordinates (6, 1). Find
the coordinates of Y.
Step 1 Let the coordinates of Y equal (x, y).
Step 2 Use the Midpoint Formula:

1-6
Example 2 Continued
Step 3 Find the x-coordinate.
Set the coordinates equal.
Multiply both sides by 2.
12 = 2 + x Simplify.
– 2 –2
10 = x
Subtract.
Simplify.
2 = 7 + y
– 7 –7
–5 = y
The coordinates of Y are (10, –5).

1-6
S is the midpoint of RT. R has coordinates
(–6, –1), and S has coordinates (–1, 1). Find
the coordinates of T.
Step 1 Let the coordinates of T equal (x, y).
Step 2 Use the Midpoint Formula:

1-6
Check It Out! Example 2 Continued
Step 3 Find the x-coordinate.
Set the coordinates equal.
Multiply both sides by 2.
–2 = –6 + x Simplify.
+ 6 +6
4 = x
Add.
Simplify.
2 = –1 + y
+ 1 + 1
3 = y
The coordinates of T are (4, 3).

1-6
The Ruler Postulate can be used to find the distance
between two points on a number line. The Distance
Formula is used to calculate the distance between
two points in a coordinate plane.

1-6
Example 3: Using the Distance Formula
Find FG and JK.
Then determine whether FG  JK.
Step 1 Find the
coordinates of each point.
F(1, 2), G(5, 5), J(–
4, 0), K(–1, –3)

1-6
Example 3 Continued
Step 2 Use the Distance Formula.

1-6
Find EF and GH. Then determine if EF  GH.
Step 1 Find the coordinates of
each point.
E(–2, 1), F(–5, 5), G(–1, –
2), H(3, 1)

1-6
Check It Out! Example 3 Continued
Step 2 Use the Distance Formula.

1-6
You can also use the Pythagorean Theorem to
find the distance between two points in a
coordinate plane. You will learn more about the
Pythagorean Theorem in Chapter 5.
In a right triangle, the two sides that form the
right angle are the legs. The side across from the
right angle that stretches from one leg to the
other is the hypotenuse. In the diagram, a and b
are the lengths of the shorter sides, or legs, of the
right triangle. The longest side is called the
hypotenuse and has length c.

1-6
Example 4: Finding Distances in the Coordinate Plane
Pythagorean Theorem to find the distance, to
the nearest tenth, from D(3, 4) to E(–2, –5).

1-6
Example 4 Continued
Method 1
Use the Distance Formula. Substitute the
values for the coordinates of D and E into the
Distance Formula.

1-6
Method 2
Use the Pythagorean Theorem. Count the units for
sides a and b.
Example 4 Continued
a = 5 and b = 9.
c2 = a2 + b2
= 52 + 92
= 25 + 81
= 106
c = 10.3

1-6
Check It Out! Example 4a
Pythagorean Theorem to find the
distance, to the nearest tenth, from R to S.
R(3, 2) and S(–3, –1)
Method 1
values for the coordinates of R and S into the
Distance Formula.

1-6
Check It Out! Example 4a Continued
R(3, 2) and S(–3, –1)

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Method 2
sides a and b.
a = 6 and b = 3.
c2 = a2 + b2
= 62 + 32
= 36 + 9
= 45
Check It Out! Example 4a Continued

1-6
Check It Out! Example 4b
R(–4, 5) and S(2, –1)
Method 1
values for the coordinates of R and S into the
Distance Formula.

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Check It Out! Example 4b Continued
R(–4, 5) and S(2, –1)

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Method 2
sides a and b.
a = 6 and b = 6.
c2 = a2 + b2
= 62 + 62
= 36 + 36
= 72
Check It Out! Example 4b Continued

1-6
A player throws the ball
from first base to a point
located between third
base and home plate and
10 feet from third base.
What is the distance of
the throw, to the nearest
tenth?
Example 5: Sports Application

1-6
Set up the field on a coordinate plane so that home
plate H is at the origin, first base F has coordinates
(90, 0), second base S has coordinates (90, 90), and
third base T has coordinates (0, 90).
The target point P of the throw has coordinates (0, 80).
The distance of the throw is FP.
Example 5 Continued

1-6
The center of the pitching
mound has coordinates
(42.8, 42.8). When a
pitcher throws the ball from
the center of the mound to
home plate, what is the
distance of the throw, to
the nearest tenth?
 60.5 ft

1-6
Lesson Quiz: Part I
(17, 13)
(3, 3)
12.7
3. Find the distance, to the nearest tenth, between
S(6, 5) and T(–3, –4).
4. The coordinates of the vertices of ∆ABC are
A(2, 5), B(6, –1), and C(–4, –2). Find the perimeter
of ∆ABC, to the nearest tenth.26.5
1. Find the coordinates of the midpoint of MN with
endpoints M(-2, 6) and N(8, 0).
2. K is the midpoint of HL. H has coordinates (1, –
7), and K has coordinates (9, 3). Find the
coordinates of L.

1-6
Lesson Quiz: Part II
5. Find the lengths of AB and CD and determine
whether they are congruent.

1013 midpointdistnaceandpythag

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1013 midpointdistnaceandpythag